Existing wired communications networks, such as, for example, the Internet, use various algorithms for disseminating routing data necessary for routing packets from a source node to a destination node. Each node of the network that handles packets needs sufficient knowledge of the network topology such that it can choose the right output interface through which to forward received packets. Link state routing algorithms, such as the Open Shortest Path First (OSPF) algorithm, permit the construction of a network topology such that any given node in the network may make packet-forwarding decisions. OSPF is defined by Internet RFC 2328, STD 54, and related documents, published by the Internet Society. OSPF is also defined by Internet RFC 2740, and related documents, also published by the Internet Society.
OSPF has conventionally been implemented in wired point-to-point or multi-access (Ethernet like) networks. It may also be highly desirable to implement OSPF over a multi-hop, multi-access packet radio network with its own private, internal routing system (such as a MANET, or “Mobile Ad-hoc NETwork”), so as to permit seamless integration of such a network into an OSPF environment, and to achieve strict compatibility between that packet radio network and standard COTS (Commercial Off-The-Shelf) routers outside that network. This can be achieved either by implementing OSPF at a higher layer over the multi-hop, multi-access packet radio network on top of that network's private, internal routing system, or by implementing both routing systems in parallel at the same network layer. In such a scheme, OSPF would be responsible for routing between the packet radio network and external hosts or networks, while the packet radio network's internal routing system would handle routing of packets within the packet radio network. Similar schemes are commonly used to implement OSPF over, for example, an X.25 packet switched network or an ATM packet network, and are well-known to practitioners of the art.
However, a number of difficulties may arise if OSPF is implemented over a multi-hop, multi-access packet radio network with its own private, internal routing system. Although the private, internal routing system of such a network may enable it to appear to OSPF much like a wired network, the properties and characteristics of such radio networks are nevertheless very different from those of wired point-to-point or multi-access networks. Like an Ethernet, such radio networks link together a large number of routers; and also like an Ethernet, such networks typically provide a suite of unicast, multicast, and netwide broadcast services. However, unlike an Ethernet, such networks possess internal structure of their own. On one hand, both unicast and multicast packets containing routing data may need to be relayed across the network by multiple lower-layer hops in accordance with the network's private routing scheme, and replicated many times in the process. On the other hand, there exist possibilities for spatial reuse in a multi-hop radio network that do not exist on an Ethernet. Consequently, the standard OSPF mechanisms for distribution of routing data may not be appropriate.
Even worse, the structure of the radio network may fluctuate and, hence, the cost of transporting routing information may be constantly changing due to radio mobility, interference, fading, and other causes. Furthermore, the capacity and reliability of such networks is typically much lower than for an Ethernet, and delays much longer; capacity is limited by the available radio bandwidth, reliability is reduced by increased risks of collisions, interface, noise, and fading, and by the possibility of transient routing inconsistencies at the lower layer; and delay is increased by the multi-hop relaying at the intranet layer.
Furthermore, the need to replicate packets within such a network for either unicast or multicast forwarding may introduce or exacerbate problems involved in scaling to networks with large numbers of nodes, especially large numbers of OSPF routers. This is especially unfortunate, as certain applications may require thousands of OSPF routers on such a network.
In particular, the adoption of the standard OSPF multi-access network “designated router” model for distribution of routing information over a multi-hop routing network is inappropriate. While the distribution of routing information from the “designated router” to other routers on the network via multicast can be made reasonably efficient, each routing advertisement must still be acknowledged back to the designated router by unicast. This, in turn, would result in an implosion of routing acknowledgements in the vicinity of the designated router that preclude scaling to large networks by exploiting spatial reuse.
Likewise, the adoption of the alternative standard OSPF point-to-multipoint network model for distribution of routing information over a multi-hop routing network is equally inappropriate. The links employed by a point-to-multipoint model to represent the radio network are likely to be several radio hops in length, and so their use to distribute routing information would often require packet replication and/or result in transmitting duplicate information over a single radio link. Furthermore, the network of links needed by a point-to-multipoint model to represent the radio network may be much more dense than required for distribution of routing information. Finally, this network of links may be constantly changing in response to the need for accurate representation of the radio network, and so may not be sufficiently stable for effective use in distributing routing information.
On the other hand, it is highly desirable to retain the basic OSPF model of reliable flooding, especially when large quantities of external, rarely-changing routing data must be carried across the radio network.
Therefore, there exists a need for systems and methods that can resolve some of the inherent problems that exist with distributing OSPF routing information across a multi-hop, multi-access packet radio network, while maintaining full compatibility with standard OSPF over other networks and preserving the basic OSPF model of reliable flooding.